Borylation of fluorinated arenes using the boron-centred nucleophile B(CN)32--a unique entry to aryltricyanoborates

Article abstract of DOI:10.1039/c7sc02249b

The potassium salt of the boron-centred nucleophile B(CN)₃^2- (1) readily reacts with perfluorinated arenes, such as hexafluorobenzene, decafluorobiphenyl, octafluoronaphthalene and pentafluoropyridine, which results in KF and the K⁺ salts of the respective borate anions with one {B(CN)₃} unit bonded to the (hetero)arene. An excess of K₂1 leads to the successive reaction of two or, in the case of perfluoropyridine, even three C-F moieties and the formation of di- and trianions, respectively. Moreover, all of the 11 partially fluorinated benzene derivatives, C₆F_6-nH_n (n = 1-5), generally react with K₂1 to give new tricyano(phenyl)borate anions with high chemo- and regioselectivity. A decreasing number of fluorine substituents on benzene results in a decrease in the reaction rate. In the cases of partially fluorinated benzenes, the addition of LiCl is advantageous or even necessary to facilitate the reaction. Also, pentafluorobenzenes R-C₆F₅ (R = -CN, -OMe, -Me, or -CF₃) react via C-F/C-B exchange that mostly occurs in the para position and to a lesser extent in the meta or ortho positions. Most of the reactions proceed via an S_NAr mechanism. The reaction of 1,4-F₂C₆H₄ with K₂1 shows that an aryne mechanism has to be considered in some cases as well. In summary, a wealth of new stable tricyano(aryl)borates have been synthesised and fully characterized using multi-NMR spectroscopy and most of them were characterised using single-crystal X-ray diffraction.

Full text of DOI:10.1039/c7sc02249b

View Article Online
View Journal
Chemical
Science
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Landmann, P. T.
Hennig, N. Ignat'ev and M. Finze, Chem. Sci., 2017, DOI: 10.1039/C7SC02249B.
This is an Accepted Manuscript, which has been through the
Volume
7 Number 1 January 2016 Pages 1–812
Royal Society of Chemistry peer review process and has been
accepted for publication.
Chemical
Science
Accepted Manuscripts are published online shortly after
www.rsc.org/chemicalscience
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2041-6539
EDGE ARTICLE
Francesco Ricci et al.
Electronic control of DNA-based nanoswitches and nanodevices
rsc.li/chemical-science

Please do not adjust margins
Chemical Science
Page 1 of 7
View Article Online
DOI: 10.1039/C7SC02249B
Journal Name
ARTICLE
Borylation of Fluorinated Arenes with the Boron-centred
Nucleophile B(CN)32− – a Unique Entry to Aryltricyanoborates†
Johannes Landmann,a Philipp T. Hennig,a Nikolai V. Ignat’ev,b and Maik Finze*a
Received 00th January 20xx,
Accepted 00th January 20xx
2−
The potassium salt of the boron-centred nucleophile B(CN)3 (1) readily reacts with perfluorinated arenes, e.g.
DOI: 10.1039/x0xx00000x
hexafluorobenzene, decafluorobiphenyl, octafluoronaphthalene or pentafluoropyridine, to result in KF and the K+ salts of
the respective borate anion with one {B(CN)3} unit bonded to the (hetero)arene. An excess of K21 leads to the successive
reaction of two or, in case of perfluoropyridine, even three C–F moieties and the formation of di- and trianions,
respectively. Moreover, all 11 partially fluorinated benzene derivatives C6F6–nHn (n = 1–5) react with K21 to give new
tricyano(phenyl)borate anions with high chemo- and regioselectivity, in general. A decreasing number of fluorine
substituents at benzene results in a decrease of the reaction rate. In case of partially fluorinated benzenes the addition of
LiCl is advantageous or even necessary to facilitate the reaction. Also, pentafluorobenzenes R–C6F5 (R = –CN, –OMe, –Me,
–CF3) react via C–F/C–B exchange that mostly occurs in para position and to a lesser extend in meta or ortho position.
Most of the reactions proceed via a SNAr mechanism. The reaction of 1,4-F2C6H4 with K21 shows that an aryne mechanism
has to be considered in some cases, as well. In summary, a wealth of new stable tricyano(aryl)borates have been
synthesised and fully characterized by multi-NMR spectroscopy and most of them by single-crystal X-ray diffraction.
www.rsc.org/
Introduction
Anionic boron-centred nucleophiles are of growing interest
since boron centres are usually electrophilic (Lewis-acidic). So,
boron-centred nucleophiles reveal an unusual reactivity and
are expected to have a large synthetic potential.1-4 The
isolation of a first boron-centred nucleophile in 2006, the
lithiated boryl anion
A that is stable in THF at –45 °C for
months, was an important development in this field that
stimulated intensive further research (Scheme 1).5 The
chemistry of the lithiated boryl anion A and closely related
species3,6-8 was studied in detail and they were found to be
versatile starting compounds for the introduction of boryl
moieties.1,3-14
Although
some
other
boron-centred
nucleophiles have been described, their number is still
limited.15-26 Boryl anions were found to be stabilized by
carbene ligands such as NHCs (NHC = N-heterocyclic carbene)
and cAACs (cAAC = cyclic (alkyl)(amino)carbene) as exemplified
27
28
by
B
and
C
(Scheme 1). An alternative approach for the
stabilization of boron-centred nucleophiles is the introduction
28
of cyano groups at boron as shown by
2–
C
and the
tricyanoborate dianion B(CN)3
(1
).29-32 The latter is the only
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 2 of 7
View Article Online
DOI: 10.1039/C7SC02249B
ARTICLE
Journal Name
dianionic boryl anion known, to date, and its alkali metal salts are known. They are either metal-catalyzed37-42 or -mediated43
are indefinitely stable at room temperature in an inert atmos- reactions or photoinduced radical borylations44-45 (Scheme 1).
phere. The first syntheses towards alkali metal salts of
started from M[B(CN)4] (M = alkali metal).29 Recently, we B(CN)3
reported on convenient, high-yield and large-scale entries arenes46-51 including perfluorinated pyridine, naphthalene and
towards salts of starting from readily available tricyano- biphenyl as well as fluorinated arenes with a functional group.
borates M[BF(CN)3]33-34 and M[BH(CN)3]35-36 (Scheme 1).30-32 All reactions proceed under exchange of fluorine against the
The unprecedented formation of dianion
from [BH(CN)3]– is tricyanoboryl moiety and most are chemo- and regioselective.
1
Herein, we report on SNAr reactions of the boryl dianion
2–
(1) with selected fully and partially fluorinated
1
1
the first example for the deprotonation of a hydridoborate Even multiple exchange reactions providing access to bis- and
anion.31-32 Conversion of a hydridoborane into monoanion
the only related reaction,28 known to date.
C
is tris(tricyanoborate) anions have been achieved.
As mentioned before, boron-centred nucleophiles reveal a
large synthetic potential. Surprisingly, only very few examples
for reactions of such nucleophiles with fluorinated arenes have
Results and Discussion
Reactions of K2B(CN)3 (K21) with perfluoropyridine.
been reported. Boryl lithium A was found to react with C6F6 or
C6H5F to the corresponding monoborylated benzenes.6 Similar
As outlined in the introduction, K2B(CN)3 (K21) was found to
27
30
react with an excess of C6F6 at room temperature in THF to
give salts of the [C6F5B(CN)3]– anion (B6a) in 67% yield.30 The
reactions have been reported for
B
and
1
with C6F6, only
(Scheme 1). In general, only a limited number of trans-
formations of C–F into C–B bonds of arenes or heteroarenes
related reaction of perfluoropyridine with K2
1
was found to
Table 1 Reactions of K21 with selected fluoro(hetero)arenes.
entry
1
substrate
C6FH5
LiCl a K21 b
yes <1
yes <1
yes <1
yes <1
yes <1
yes <1
yes <1
yes <1
yes <1
conditions
80 °C, 2 d
r.t., 16 h
r.t., 3 d
[BH(CN)3]− c major tricyanoborate anion(s) formed
isolated yield
45%
25%
9%
<5%
28%
<5%
<5%
<5%
<5%
<5%
10%
30%
n.d.
10%
48%
-
[1-{(NC)3B}-C6H5]− (B1)
sole isomer
sole isomer
sole isomer
2
1,2-C6F2H4
1,3-C6F2H4
1,4-C6F2H4
1,2,3-C6F3H3
1,2,4-C6F3H3
1,3,5-C6F3H3
1,2,3,4-C6F4H2
1,2,3,5-C6F4H2
1,2,3,5-C6F4H2
1,2,4,5-C6F4H2
1,2,4,5-C6F4H2
C6F5H
[1-{(NC)3B}-2-F-C6H4]− (B2a)
[1-{(NC)3B}-3-F-C6H4]− (B2b)
[1-{(NC)3B}-4-F-C6H4]− (B2c) + B2b (6:4d) e
58%
3
70%
45% e
4
75 °C, 30 h
r.t., 3 d
5
[1-{(NC)3B}-2,3-F2-C6H3]− (B3a) + [1-{(NC)3B}-2,6-F2-C6H3]− (B3b) (4:1)
66%
6
r.t., 2 h
[1-{(NC)3B}-2,5-F2-C6H3]− (B3c)
[1-{(NC)3B}-3,5-F2-C6H3]− (B3d)
[1-{(NC)3B}-2,3,6-F3-C6H2]− (B4a)
[1-{(NC)3B}-2,3,5-F3-C6H2]− (B4b)
B4b
[1-{(NC)3B}-2,4,5-F3-C6H2]− (B4c)
[1,4-{(NC)3B}2-2,5-F2-C6H2]2− (B4d)
[1-{(NC)3B}-2,3,5,6-F4-C6H]− (B5)
B5
[1-{(NC)3B}-C6F5]− (B6a) 29
[1,4-{(NC)3B}2-C6F4]2− (B6b)
[4-{(NC)3B}-C5F4N]– (Py1) g
[2,4-{(NC)3B}2-C5F3N]2– (Py2) i
[2,4,6-{(NC)3B}3-C5F2N]3– (Py3)
[4-{(NC)3B}-C12F9]− (BP1)
[4,4’-{(NC)3B}2-C12F8]2− (BP2)
[2-{(NC)3B}-C10F7]– (N1)
sole isomer
76%
7
r.t., 16 h
r.t., <1 h
r.t., 2 h
sole isomer
63%
8
sole isomer
77%
9
sole isomer
63%
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
no
yes <1
yes
yes <1
<1
75 °C, 30 h
r.t., 30 min
r.t., 16 h
r.t., 10 min
r.t., 2 d
8% of other isomers
sole isomer
51%
50%
42% f
2
sole isomer
6% of one other isomer
20% of other anions
sole isomer
62%
C6F5H
no
no
no
no
no
no
no
no
no
no
no
no
no
no
no
no
<1
<1
2.2
0.33
2
39%
67% 30
C6F6
0 °C
C6F6
reflux, 20 h
r.t., 12 h
r.t., 4 d
-
sole isomer
74%
C5F5N
-
other isomer(s), Py2, Py3
other isomer(s), Py3
<10% Py1 and Py2
<20% of BP2
81% h
59% j
31%
C5F5N
-
C5F5N
3
r.t., 4 d
-
C12F10
0.8
2.2
0.5
2
r.t., 2 h
-
49%
C12F10
50 °C, 1 h
r.t., 3 d
-
sole isomer
90%
C10F8
-
8% of other isomersk
mixture of N1, N2 and N3l
sole isomer
55%
C10F8
60 °C, 16 h
r.t., 3 h
-
[2,6-{(NC)3B}2-C10F6]2– (N2)
24%
F3C-C6F5
<1
<1
<1
<1
<1
<1
-
[1-F3C-4-{(NC)3B}-C6F4]– (B7)
[1-Me-4-{(NC)3B}-C6F4]– (B8a) + [1-Me-3-{(NC)3B}-C6F4]– (B8b) (9:1)
68%
Me-C6F5
90 °C, 3 d
r.t., 2 h
-
n.d.
1-F3C-4-H-C6F4
1-F3C-6-H-C6F4
MeO-C6F5
NC-C6F5
75%
2%
-
unidentified borate anions
[1-F3C-4-{(NC)3B}-2,3,5-F3-C6H]− (B9)
[1-MeO-4-{(NC)3B}-C6F4]– (B10a) + [1-MeO-3-{(NC)3B}-C6F4]– (B10b) (1:1) 82%
[1-NC-4-{(NC)3B}-C6F4]– (B11a) + [1-NC-2-{(NC)3B}-C6F4]– (B11b) +
[B(CN)4]− (2.5:1.5:1) m
n.d.
r.t. 4 d
7% of other isomers
78%
60 °C, 16 h
r.t., <1 h
-
n.d.
30
31
Cl-C6F5
no
no
<1
<1
r.t., <1 h
r.t., 16 h
-
-
[BCl(CN)3]−, [B2(CN)6]2−, …
[B2(CN)6]2−, …
n.d.
n.d.
O2N-C6F5
a
b
c
d
LiCl added to the reaction mixture. Equivalents of K21. Formed as side product; [BH(CN)3]− was removed during work-up. Ratio of B2c:B2b in the reaction
mixture: 6:4; in the isolated material: 7:3. e 11% of K[BH(CN)3]. f [Et3NH]+ salt. g Py1 was formed in 75% internal yield; 16% of Py2, 8% of another isomer (probably [2-
{(NC)3B}-C5F4N]–), 1% of Py3 and unknown tricyano(fluoropyridinyl)borate anions. Purity ca. 85% (11B/19F NMR); contained 15% of other tricyano(fluoropyridinyl)-
h
borates.
j
i Internal yield (11B/19F NMR) of Py2: 60%; 30% of Py3, 10% of another tricyano(fluoropyridinyl)borate anion. Purity ca. 75% (11B/19F NMR); contained 15% of K3Py3
and 10% of another tricyano(fluoropyridinyl)borate. N2:N3 = 1.0:0.8 (N3 = [2,7-{(NC)3B}2-C10F6]2–). Ratio in the reaction mixture: N1:N2:N3 = 0.4:1.0:0.7; N2 is
k
l
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 3 of 7
View Article Online
DOI: 10.1039/C7SC02249B
Journal Name
ARTICLE
An excess of K2
1
yielded larger amounts of dianion Py2 and
trianion Py3 and the reaction of perfluoropyridine with two
equivalents of K2 gave K2Py2 as major product. Three equiva-
1
lents of the potassium salt resulted in K3Py3 in 31% yield. A
related, successive replacement of 1, 2 and 3 fluorine sub-
stituents of perfluoropyridine via nucleophilic replacement
was reported for the methoxy anion, earlier.54 In contrast, alkyl
and aryl Grignard reagents were reported to result in mono-
substitutions in para position of perfluoropyridine, solely.55
The decreasing solubility of the potassium borates KPy1, K2Py2
and K3Py3 with increasing charge of the anion enabled the
enrichment of K2Py2 and the purification of K3Py3 by precipi-
tation from THF solutions by slow addition of CH2Cl2. Pure
KPy1 and K2Py2 were obtained by crystallization. Single-
crystals of KPy1, K2Py2·OC(CH3)2 and K3Py3·3THF·1.04H2O
were studied by X-ray diffraction (Figure 1). Selected
experimental bond distances of the three related anions Py1
Py2 and Py3 are compared to calculated bond lengths in Table
S3
,
†.
Monosubstitution of partly fluorinated benzenes with K21.
In addition to the reactions of K2
with hexafluorobenzene30
and pentafluoropyridine, K2 was found to undergo C–F/C–B
start already at temperatures below 0 °C as evident from the
rapid decolorization of the suspension. The [4-{(NC)3B}-C5F4N]–
anion (Py1) was obtained as the main product of the reaction
with an excess of perfluoropyridine (Table 1, Figure 1).
Exchange of fluorine in the 4-position is typical for SNAr
1
1
exchange reactions with all partly fluorinated benzenes C6F6–
nHn (n = 1–5) (Table 1, Figure 2). Unprecedentedly, nucleophilic
attack of
1 at almost all partially fluorinated benzenes is regio-
reactions of C5F5N.52-55 Dianion [2,4-{(NC)3B}2-C5F3N]2–
(Py2), a
and chemoselective. As expected for electron deficient partly
fluorinated benzenes, deprotonation was observed by the
different isomer of Py1, most likely [2-{(NC)3B}-C5F4N]–, and
1
yielding [BH(CN)3]– as side product. The amount
small amounts (<1%) of further tricyano(fluoropyridinyl)borate
anions including the trianion [2,4,6-{(NC)3B}3-C5F3N]3–
have been obtained as side products.
strong base
of [BH(CN)3]– formed, reflects the Brønsted acidity of the
hydrogen atoms of the respective fluorobenzene.56-57 1,2,4,5-
(Py3)
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 4 of 7
View Article Online
DOI: 10.1039/C7SC02249B
ARTICLE
Journal Name
induced reaction was successfully applied for all di- and
trifluorobenzenes and C6FH5 (Figure 1). Reactions of all three
trifluorobenzene isomers and of 1,2- as well as 1,3-difluoro-
benzene were performed at room temperature. Only for 1,4-
F2-C6H4 and C6FH5 higher temperatures were necessary. Three
different effects may be responsible for the faster reactions
and the higher chemo- and regioselectivities in the presence of
LiCl: (i) Li2
1
is more soluble in THF than K21 31
. (ii) The high fluoride ion
, which results in
an enhanced availability of dianion
1
affinity of Li+ may lead to a Li···F interaction, a weakening of
the C–F bond and a lowering of the activation barrier for the
nucleophilic replacement. (iii) A weak Li···B or Li···N interaction
between Li+ and boryl dianion
1 may influence the reactivity of
tetrafluoro- and pentafluorobenzene gave the largest amounts
of [BH(CN)3]– with up to 48% for C6F5H (Table 1). Addition of
1.
LiCl at the start of the reaction of K2
reduction of the amount of [BH(CN)3]– to 10% and in an
increased yield of [1-{(NC)3B}-2,3,5,6-F4-C6H]−
B5) of 62%.
1 with C6F5H resulted in a
Disubstitution of fluorinated benzenes with K21.
(
C6F6 and 1,2,4,5-F4-C6H2 were reacted with an excess of K21 to
give salts of the dianions [1,4-{(NC)3B}2-C6F4]2–
Since the salts [(alkyl)3NH][BH(CN)3] (alkyl = Me, Et) are water
soluble, purification was achieved via precipitation or
extraction of the respective trimethyl- or triethylammonium
phenylborates from aqueous solutions. The ammonium salts
were easily back-converted into K+ salts with K2CO3.
(
B6b) and [1,4-
{(NC)3B}2-2,6-F2-C6H2]2–
(B4d) (Table 1, Figure 2). In case of the
reaction of 1,2,4,5-F4-C6H2 anhydrous LiCl was added to enhan-
ce the rate of reaction. Both reactions were found to be highly
regioselective and in accordance to a SNAr mechanism. So, the
second C–F/C–B exchange gave the para-{B(CN)3}2 derivatives
as sole isomers.
The regioselectivities of the C–F/C–B exchange reactions
were found to be high and in most cases one major isomer had
formed (Table 1). Most of the new tricyanoborates were
characterized by single-crystal X-ray diffraction (Figure 2) and
details of the experimental and calculated bond parameters
In addition to the multiple C–F/C–B exchange reactions of
C5F5N (Figure 1), C6F6 and 1,2,4,5-F4-C6H2 (Figure 2), perfluoro-
biphenyl and perfluoronaphthalene were successfully applied
are summarized in Table S3†. Exchange of fluorine against a
tricyanoboryl group in para position to a fluorine substituent is
unfavoured. Replacement was found to be preferred for
fluorine substituents in meta position to one or two further
fluorine substituents, which is typical for SNAr reactions of flu-
orobenzenes.52-53 1,4-difluorobenzene gave a mixture of [1-
{(NC)3B}-4-F-C6H4]– B2c) and [1-{(NC)3B}-3-F-C6H4]–
( (B2b) in
conjunction with 25% of [BH(CN)3]− (Scheme 2). Formation of
anion B2b is rationalized by an aryne mechanism similar to
related reactions.58 In summary, the high regioselectivities
observed show that a SNAr mechanism dominates for the C–
F/C–B exchange presented herein.
The reaction rate of the C–F/C–B exchange strongly
depended on the degree of fluorination and therefore on the
electron density of the aromatic ring system. C6F6 reacted
within minutes at room temperature whereas the conversion
of C6F5H required two days. In case of mono-, di- and trifluoro-
benzenes no reaction was observed with K2
1 in THF even at 80
°C. Tetrafluorobenzenes showed some reactivity towards K2
1
in THF depending on the substitution scheme. 1,2,3,5-tetra-
fluorobenzene reacted at 75 °C within 3 days. The reaction of
the 1,2,4,5-isomer required 120 °C yielding an inseparable
brownish mixture. The addition of anhydrous LiCl was found to
result in a tremendous increase in the reaction rate. For
example, upon addition of LiCl a mixture of 1,2,4,5-tetrafluoro-
benzene and K21 immediately became warm and the reaction
was complete within minutes. Similarly, the reaction time of
the conversion of C6F5H into B5 was reduced from 2 days to 10
minutes. The shorter reaction time was accompanied by an
enhanced chemo- and regioselectivity (Table 1). The LiCl-
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 5 of 7
View Article Online
DOI: 10.1039/C7SC02249B
Journal Name
ARTICLE
in related reactions with K21. Stoichiometric amounts or a unidentified borate anions had formed. In contrast, 1-F3C-2-H-
slight excess of K2
yielded K2[4,4’-{(NC)3B}2-C12F8] (K2BP2) and C6F4 and K21 gave the [1-F3C-4-{(NC)3B}-2,3,5-F3-C6H]− anion
K2[2,6-{(NC)3B}2-C10F6] (K2N2), respectively. In contrast, an
B9) in 78% yield and only 2% of [BH(CN)3]– were observed
excess of the perfluorinated arene predominantly gave the (Table 1).
corresponding monoanions [4-{(NC)3B}-C12F9]–
BP1) and [2- The reactions of K2
{(NC)3B}-C10F7]–
N1) (Table 1). The successive reactions of complex product mixtures and the hexacyanoborate dianion
1
(
(
1 with Cl-C6F5 and O2N-C6F5 gave
(
perfluorobiphenyl to give BP1 and BP2 are fully regioselective. [B2(CN)6]2– 59 was identified. Additionally, the tricyano-
K2BP2 was isolated in an excellent yield of 90% and a single- haloborate anion [BCl(CN)3]– 60 formed from Cl-C6F5 (Table 1).
crystal was investigated by X-ray diffraction (Figure 3, Table
S3
for the first replacement of fluorine against
naphthalene to give N1. The introduction of a second {B(CN)3}
moiety resulted in a mixture of N1 N2 and [2,7-{(NC)3B}2-
C10F6]2–
N3) with a ratio of 0.4:1.0:0.7. The formation of N2 as
†
). A slightly lower but still high regioselectivity was found
Conclusions
1
in perfluoro-
Boron-centred nucleophiles are an emerging class of com-
pounds and are of growing importance for synthetic chemistry
because they provide a very convenient entry to boron-
functionalized compounds and materials.1-28 The unprecedent-
ed, straightforward, regioselective and transition-metal-free
introduction of one, two or even three {B(CN)3}– units into
fluoro(hetero)arenes starting from easily accessible K2130-32
opens up an unique and convenient access to single and
multiple charged anions with tricyanoborate moieties. The
observed regioselectivities for the C–F/C–B exchange reactions
are almost all in accordance with a SNAr mechanism, which
,
(
the major isomer agrees to the substitution scheme typical for
SNAr reactions of perfluoronaphthalene.53
Reactions of K21 with fluorinated benzenes with functional
groups.
The reactions described, so far (vide supra), exemplify the
regioselectivity of the SNAr reaction of fluorinated
(hetero)arenes with K21 and show the possibility to synthesise
multiple charged tricyanoborate anions. The multiple C–F/C–B
exchange reactions are first examples for transformations of
shows the boron-centred nucleophilic character of dianion 1 as
observed for the formation of [B2(CN)6]2– starting from K21 and
K[BF(CN)3], earlier.59 So, an alternative radical reaction
pathway is highly unlikely, although this type of reactivity was
observed for other boron-centred nucleophiles.61-62 Further-
functionalized fluorinated (hetero)arenes with 1. A series of
further selected reactions of polyfluorinated benzenes with a
functional group bonded to the benzene ring have been
studied (Figure 4, Table 1, entries 24–31).
Perfluorotoluene was found to give [1-F3C-4-{(NC)3B}-C6F4]–
more, the syntheses highlight the value of K2
1 for the
(
B7) as sole isomer and KB7 was isolated in 68% yield. 4-Me-
C6F5 resulted in a mixture of the isomers [1-Me-4-{(NC)3B}-
C6F4]– B8a) and [1-Me-3-{(NC)3B}-C6F4]–
B8b) in a 9:1 ratio
and pentafluoroanisole gave [1-MeO-4-{(NC)3B}-C6F4]–
B10a
and [1-MeO-3-{(NC)3B}-C6F4]–
B10b) in equal amounts. The
preparation of a wealth of tricyanoborate anions, in general.
Since salts of tricyanoborate anions such as the ones described
herein are promising building blocks for materials science, for
example as component of ionic liquids used in electrochemical
devices,63 convenient and high yield syntheses are necessary
to facilitate applications.
(
(
(
)
(
decrease in regioselectivity in the order F3C-C6F5, Me-C6F5 and
MeO-C6F5 reflects the influence of the electronic properties of
the substituents –CF3, –Me and –OMe on the reactivity of the
corresponding fluoroarenes. The trifluoromethyl group is a
strong electron withdrawing group while the methoxy group is
an electron donating group. Strong electron withdrawing
groups are usually para and ortho directing. Most likely, steric
effects are the reason that the ortho-substituted product [1-
F3C-2-{(NC)3B}-C6F4]– was not observed. The reaction of K21
with NC-C6F5, which contains the strong electron withdrawing
cyano group that is sterically less demanding than the CF3
group, gave the ortho-substituted anion [1-NC-2-{(NC)3B}-
C6F4]– (B11b) together with [1-NC-4-{(NC)3B}-C6F4]– (B11a) and
[B(CN)4]− in a ratio of 1.5:2.5:1. The formation of the
tetracyanoborate anion is due to nucleophilic attack at the
carbon atom of the cyano group. Formation of [B(CN)4]−
starting from K21 was reported earlier, e.g. reactions with
(CN)2 and PhOCN.31 Single-crystals of the potassium salts of [1-
F3C-4-{(NC)3B}-C6F4]– (B7), [1-MeO-4-{(NC)3B}-C6F4]– (B10a) and
Acknowledgements
The authors are grateful to Merck KGaA (Darmstadt, Germany)
for generous support.
Notes and references
1
M. Yamashita, K. Nozaki, in Topics in Organometallic Chemistry:
Synthesis and Application of Organoboron Compounds (Eds.: E.
Fernández, A. Whiting), Springer, Cham, Switzerland, 2015, pp.
1–37.
2
J. Cid, H. Gulyás, J. J. Carbó, E. Fernández, Chem. Soc. Rev.,
2012, 41, 3558–3570.
3
4
5
M. Yamashita, Bull. Chem. Soc. Jpn., 2011, 84, 983–999.
L. Weber, Eur. J. Inorg. Chem., 2012, 5595–5609.
Y. Segawa, M. Yamashita, K. Nozaki, Science, 2006, 314, 113–
115.
[1-NC-4-{(NC)3B}-C6F4]–
(
B11a
)
were characterized by
6
Y. Segawa, Y. Suzuki, M. Yamashita, K. Nozaki, J. Am. Chem. Soc.,
2008, 130, 16069–16079.
diffraction experiments (Figure 4, Table S3†).
Deprotonation of 1-F3C-4-H-C6F4 to give [BH(CN)3]– was
found to be the most relevant reaction with K21 and other
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Chemical Science
Page 6 of 7
View Article Online
DOI: 10.1039/C7SC02249B
ARTICLE
Journal Name
7
8
9
M. Yamashita, Y. Suzuki, Y. Segawa, K. Nozaki, J. Am. Chem. Soc., 34 N. Ignatyev, J. A. P. Sprenger, J. Landmann, M. Finze, Merck
2007, 129, 9570–9571. Patent GmbH, WO2014198401, 2014.
Y. Okuno, M. Yamashita, K. Nozaki, Angew. Chem. Int. Ed., 2011, 35 L. A. Bischoff, M. Drisch, C. Kerpen, P. T. Hennig, J. Landmann, J.
50, 920–923. A. P. Sprenger, N. Ignat'ev, M. Finze, in preparation.
N. Dettenrieder, Y. Aramaki, B. M. Wolf, C. Maichle-Mössmer, X. 36 M. Drisch, L. A. Bischoff, L. Herkert, J. A. P. Sprenger, M. Finze,
Zhao, M. Yamashita, K. Nozaki, R. Anwander, Angew. Chem. Int.
Ed., 2014, 53, 6259–6262.
N. Ignatyev, R. van Hal, Merck Patent GmbH, WO2016074760,
2016.
10 H. Hayashi, Y. Segawa, M. Yamashita, K. Nozaki, Chem. 37 W.-H. Guo, Q.-Q. Min, J.-W. Gu, X. Zhang, Angew. Chem. Int.
Commun., 2011, 47, 5888–5890. Ed., 2015, 54, 9075–9078.
11 K. Nozaki, Y. Aramaki, M. Yamashita, S.-H. Ueng, M. Malacria, E. 38 J. Zhou, M. W. Kuntze-Fechner, R. Bertermann, U. S. D. Paul, J.
Lacôte, D. P. Curran, J. Am. Chem. Soc., 2010, 132, 11449–
11451.
H. J. Berthel, A. Friedrich, Z. Du, T. B. Marder, U. Radius, J. Am.
Chem. Soc., 2016, 138, 5250–5253.
12 A. Rit, J. Campos, H. Niu, S. Aldridge, Nature Chem., 2016, 8, 39 T. Niwa, H. Ochiai, Y. Watanabe, T. Hosoya, J. Am. Chem. Soc.,
1022–1026. 2015, 137, 14313–14318.
13 A. V. Protchenko, D. Dange, A. D. Schwarz, C. Y. Tang, N. Phillips, 40 X.-W. Liu, J. Echavarren, C. Zarate, R. Martin, J. Am. Chem. Soc.,
P. Mountford, C. Jones, S. Aldridge, Chem. Commun., 2014, 50,
3841–3844.
14 A. V. Protchenko, D. Dange, J. R. Harmer, C. Y. Tang, A. D.
2015, 137, 12470–12473.
41 S. I. Kalläne, M. Teltewskoi, T. Braun, B. Braun, Organometallics,
2015, 34, 1156–1169.
Schwarz, M. J. Kelly, N. Phillips, R. Tirfoin, K. H. Birjkumar, C. 42 M. Teltewskoi, J. A. Panetier, S. A. Macgregor, T. Braun, Angew.
Jones, N. Kalsoyannis, P. Mountford, S. Aldridge, Nature Chem.,
2014, 6, 315—319.
15 B. Wang, Y. Li, R. Ganguly, H. Hirao, R. Kinjo, Nat. Commun.,
2016, 7, 11871.
16 W. Lu, H. Hu, Y. Li, R. Ganguly, R. Kinjo, J. Am. Chem. Soc., 2016,
138, 6650–6661.
17 H. Braunschweig, C.-W. Chiu, K. Radacki, T. Kupfer, Angew.
Chem. Int. Ed., 2010, 49, 2041-2044.
18 H. Braunschweig, M. Burzler, R. D. Dewhurst, K. Radacki,
Angew. Chem. Int. Ed., 2008, 47, 5650–5653.
19 H. Braunschweig, R. D. Dewhurst, L. Pentecost, K. Radacki, A.
Vargas, Q. Ye, Angew. Chem. Int. Ed., 2016, 55, 436–440.
Chem. Int. Ed., 2010, 49, 3947–3951.
43 R. J. Lindup, T. B. Marder, R. N. Perutz, A. C. Whitwood, Chem.
Commun., 2007, 3664–3666.
44 A. M. Mfuh, J. D. Doyle, B. Chhetri, H. D. Arman, O. V. Larionov,
J. Am. Chem. Soc., 2016, 138, 2985–2988.
45 K. Chen, M. S. Cheung, Z. Lin, P. Li, Org. Chem. Front., 2016, 3,
875–879.
46 T. Ahrens, J. Kohlmann, M. Ahrens, T. Braun, Chem. Rev., 2015,
115, 931–972.
47 E. Clot, O. Eisenstein, N. Jasim, S. A. Macgregor, J. E. McGrady,
R. N. Perutz, Acc. Chem. Res., 2011, 44, 333–348.
48 H. Amii, K. Uneyama, Chem. Rev., 2009, 109, 2119–2183.
20 R. Kinjo, B. Donnadieu, M. A. Celik, G. Frenking, G. Bertrand, 49 D. O'Hagan, Chem. Soc. Rev., 2008, 37, 308–319.
Science, 2011, 333, 610–613. 50 T. G. Richmond, Angew. Chem. Int. Ed., 2000, 39, 3241–3244.
21 D. A. Ruiz, M. Melaimi, G. Bertrand, Chem. Commun., 2014, 50, 51 W. Chen, C. Bakewell, M. R. Crimmin, Synthesis, 2017, 49, 810–
7837–7839. 821.
22 L. Kong, Y. Li, R. Ganguly, D. Vidovic, R. Kinjo, Angew. Chem. Int. 52 G. M. Brooke, J. Fluorine Chem., 1997, 86, 1–76.
Ed., 2014, 53, 9280–9283.
23 L. Kong, R. Ganguly, Y. Li, R. Kinjo, Chem. Sci., 2015, 6, 2893–
53 R. D. Chambers, W. K. R. Musgrave, J. S. Waterhouse, D. L. H.
Williams, J. Chem. Soc., Chem. Commun., 1974, 239–240.
54 V. V. Aksenov, V. M. Vlasov, G. G. Yakobson, J. Fluorine Chem.,
1982, 20, 439–458.
55 Y. Sun, H. Sun, J. Jia, A. Du, X. Li, Organometallics, 2014, 33,
1079–1081.
2902.
24 D. Wu, L. Kong, Y. Li, R. Ganguly, R. Kinjo, Nat. Commun., 2015,
6, 7340.
25 T. Imamoto, T. Hikosaka, J. Org. Chem., 1994, 59, 6753–6759.
26 L. Kong, W. Lu, L. Yongxin, R. Ganguly, R. Kinjo, Inorg. Chem., 56 M. Schlosser, E. Marzi, Chem. Eur. J., 2005, 11, 3449–3454.
2017, 56, 5586–5593.
57 H. H. Büker, N. M. M. Nibbering, D. Espinosa, F. Mongin, M.
27 J. Monot, A. Solovyev, H. Bonin-Dubarle, É. Derat, D. P. Curran,
Schlosser, Tetrahedron Lett., 1997, 38, 8519–8522.
M. Robert, L. Fensterbank, M. Malacria, E. Lacôte, Angew. 58 C. Wu, F. Shi, Asian J. Org. Chem., 2013, 2, 116–125.
Chem. Int. Ed., 2010, 49, 9166–9169.
28 D. A. Ruiz, G. Ung, M. Melaimi, G. Bertrand, Angew. Chem. Int.
Ed., 2013, 52, 7590–7592.
59 J. Landmann, J. A. P. Sprenger, M. Hailmann, V. Bernhardt-
Pitchougina, H. Willner, N. Ignat'ev, E. Bernhardt, M. Finze,
Angew. Chem. Int. Ed., 2015, 54, 11259–11264.
29 E. Bernhardt, V. Bernhardt-Pitchougina, H. Willner, N. V. 60 J. A. P. Sprenger, L. A. Bischoff, M. Drisch, L. Herkert, M. Finze,
Ignatiev, Angew. Chem. Int. Ed., 2011, 50, 12085–12088.
30 J. Landmann, J. A. P. Sprenger, R. Bertermann, N. Ignat’ev, V.
H. Willner, E. Bernhardt, N. Ignatyev, M. Schulte, Merck Patent
GmbH, WO2016058665, 2016.
Bernhardt-Pitchougina, E. Bernhardt, H. Willner, M. Finze, 61 R. Bertermann, H. Braunschweig, R. D. Dewhurst, C. Hörl, T.
Chem. Commun., 2015, 51, 4989–4992.
Kramer, I. Krummenacher, Angew. Chem. Int. Ed., 2014, 53,
31 J. Landmann, F. Keppner, D. B. Hofmann, J. A. P. Sprenger, M.
5453–5457.
Häring, S. H. Zottnick, K. Müller-Buschbaum, N. V. Ignat'ev, M. 62 D. P. Curran, A. Boussonnière, S. J. Geib, E. Lacôte, Angew.
Finze, Angew. Chem. Int. Ed., 2017, 56, 2795–2799. Chem. Int. Ed., 2012, 51, 1602–1605.
32 J. Landmann, F. Keppner, J. A. P. Sprenger, M. Finze, N. Ignat'ev, 63 N. V. Ignat’ev, M. Finze, J. A. P. Sprenger, C. Kerpen, E.
Julius-Maximilians-Universität Würzburg, Merck Patent GmbH,
DE102014018103A1, 2016.
Bernhardt, H. Willner, J. Fluorine Chem., 2015, 177, 46–54.
1
33 J. A. P. Sprenger, J. Landmann, M. Drisch, N. Ignat’ev, M. Finze,
Inorg. Chem., 2015, 54, 3403–3412.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 7
Chemical Science
View Article Online
DOI: 10.1039/C7SC02249B
2–
SNAr reactions of the tricyanoboryl dianion B(CN)3 with selected fluoroarenes and
perfluoropyridine resulted in a wealth of new tricyanoarylborate anions in high yields
as well as high chemo- and regioselectivity and multiple borylation reactions provide a
valuable access to novel di- and trianions.